HOL的多表查询——内连接、外连接
2024-10-07 06:52:41
1、内连接：
由于学生和班级是多对一的关系，班级对应学生是一对多的关系，因此，需要先对学生和班级进行配置。
（1）创建Student类（多的一方）：
package pers.zhb.domain;
public class Student {
private int studentno;
private String sname;
private String sex;
private String birthday;
private String classno;
private Float point;
private String phone;
private Clas aClas;
public Student(){//无参的构造方法
}
public Clas getaClas() {
return aClas;
}
public void setaClas(Clas aClas) {
this.aClas = aClas;
}
public int getStudentno() {
return studentno;
} public void setStudentno(int studentno) {
this.studentno = studentno;
} public String getSname() {
return sname;
} public void setSname(String sname) {
this.sname = sname;
} public String getSex() {
return sex;
} public void setSex(String sex) {
this.sex = sex;
} public String getBirthday() {
return birthday;
} public void setBirthday(String birthday) {
this.birthday = birthday;
} public String getClassno() {
return classno;
} public void setClassno(String classno) {
this.classno = classno;
} public float getPoint() {
return point;
} public void setPoint(float point) {
this.point = point;
} public String getPhone() {
return phone;
} public void setPhone(String phone) {
this.phone = phone;
} @Override
public String toString() {
return "Student{" +
"studentno='" + studentno + '\'' +
", sname='" + sname + '\'' +
", sex='" + sex + '\'' +
", birthday='" + birthday + '\'' +
", classno='" + classno + '\'' +
", point=" + point +
", phone='" + phone + '\'' +
'}';
}
}
配置文件：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
<class name="Student" table="student">
<id name="studentno" column="studentno">
<generator class="native"></generator>
</id>
<property name="birthday" column="birthday"></property>
<property name="classno" column="classno" insert="false" update="false"></property>
<property name="phone" column="phone"></property>
<property name="sex" column="sex"></property>
<property name="sname" column="sname"></property>
<property name="point" column="point"></property>
<many-to-one name="aClas" column="classno" class="Clas"></many-to-one>
</class>
</hibernate-mapping>
（2）创建Clas类（班级，代表1的一方）：
package pers.zhb.domain;
import java.util.HashSet;
import java.util.Set;
public class Clas {
private String classno;
private String department;
private String monitor;
private String classname;
private Set<Student> students=new HashSet<Student>();//使用set集合表达一对多关系,一个班级对应多个学生
public String getClassno() {
return classno;
} public void setClassno(String classno) {
this.classno = classno;
} public String getDepartment() {
return department;
} public void setDepartment(String department) {
this.department = department;
} public String getMonitor() {
return monitor;
} public void setMonitor(String monitor) {
this.monitor = monitor;
}
public void setClassname(String classname) {
this.classname = classname;
}
public String getClassname() {
return classname;
} public Set<Student> getStudents() {
return students;
} public void setStudents(Set<Student> students) {
this.students = students;
} @Override
public String toString() {
return "Clas{" +
"classno=" + classno +
", department='" + department + '\'' +
", monitor='" + monitor + '\'' +
", classname='" + classname + '\'' +
", students=" + students +
'}';
} }
配置文件：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pers.zhb.domain">
<class name="Clas" table="class">
<id name="classno" column="classno">
<generator class="native"></generator>
</id><!--主键-->
<property name="department" column="department"></property>
<property name="monitor" column="monitor"></property>
<property name="classname" column="classname"></property>
<set name="students" table="student"><!--一对多关系配置-->
<key column="classno" update="false"></key><!--指定了集合表的外键-->
<one-to-many class="Student"></one-to-many>
</set>
</class>
</hibernate-mapping>
（3）测试HQL的内连接：
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from Clas c inner join c.students";
Query query=session.createQuery(hql);
List<Object[]> list=query.list();
for(Object[] arr:list){
System.out.println(Arrays.toString(arr));
}
transaction.commit();
session.
表中数据：
学生表：
班级表：
测试结果：
通过SQL语句直接查询：
SELECT *
FROM student,class
WHERE student.classno=class.classno
AND student.classno='tx171'
（4）迫切内连接：
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from Clas c inner join fetch c.students";
Query query=session.createQuery(hql);
List<Clas> list=query.list();
transaction.commit();
session.close();//游离状态
}
与内连接不同的是，迫切内连接是把学生对象直接封装到了班级对象中了，而内连接则是将两个对象存储到了数组中。
2、外连接：
（1）左外连接：
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from Clas c left join c.students";
Query query=session.createQuery(hql);
List<Clas> list=query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
（2）右外连接：
public static void testSel() {
Session session = HibernateUtils.openSession();
Transaction transaction = session.beginTransaction();
String hql="from Clas c right join c.students";
Query query=session.createQuery(hql);
List<Clas> list=query.list();
System.out.println(list);
transaction.commit();
session.close();//游离状态
}
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